Maintenance of euglycemia is crucial because glucose is the sole nutrient that can be utilized by the brain, retina, and germinal epithelium in sufficient quantities to provide required levels of energy. Since carbohydrate reserves in neural tissue are limited, normal nerve cell function depends upon a continuous glucose supply. Neurons located in select brain sites, including the hindbrain nucleus tractus solitarius/area postrema complex (NTS/AP), exhibit electrophysiological and/or genomic responses to glucopenia, suggesting that regulatory signaling of this substrate fuel deficit originates within these select loci. Fundamental questions concerning the identification of monitored metabolic variables and the molecular mechanisms by which local "sensor" cells transduce energetic disturbances into neural signals remain unresolved. Microbeam particle-induced X-ray emission spectrometry (PIXE) is the sole available investigative technique that offers multi-elemental quantitation at ppm sensitivities, with high accuracy at spatial resolutions less than cellular dimensions. The proposed project will develop nuclear microprobe analytical techniques for use with established neuroanatomical and pharmacological approaches in a novel strategy to characterize electrolytic indices of neuronal function, in defined cell populations within central metabolic "sensor" sites, in response to in vivo manipulation of glucose availability. Micron-level resolution and scanning transmission imaging capabilities of microbeam offer the possibility that quantitative spatial imaging of intracellular ion concentrations in "glucose-sensitive" brain sites can be generated. It is anticipated that innovative technique refinements will permit regional mapping, at the single cell level, of effects of glucose deficits on transmembrane flux of ions, e.g. Na, K, Cl, and Ca, that regulate neuronal membrane potential and synaptic firing. Development of complementary immunocytochemical methods for demonstration of cytoplasmic neurotransmitters, nuclear transcription factors, and retrograde labels is expected to yield important new information on phenotypic identification, genomic responsiveness, and neuroanatomical connectivity of "glucose-sensor" neurons. This research will significantly advance current understanding of the cellular and molecular bases linking neuronal energetics with homeostatic regulation of glucose availability.